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Fittingly for a story about rain, it begins with a leak. On January 2, the British newspaper The Sunday Times claimed that at the height of last summer a Swiss company had conjured heavy rainfall out of the clear blue skies of Al Ain. Meteo Systems International was said to have created rain clouds by using five batteries of giant ionisers - depicted in a graphic that accompanied the article as 10-metre-tall umbrellas with their fabric removed - to fire electrons into the sky. Carried high into the atmosphere by warm desert air, the negatively charged particles caused moisture to gather into clouds. Or so the theory went.

The government of the UAE has funded an entirely unrelated cloud seeding programme in Al Ain for more than a decade, but this separate development would, if true, represent an astonishing breakthrough in a country with almost no natural supplies of water and an expensive thirst for desalination.

According to a recent report by Global Water Intelligence, the UAE currently spends $800 million a year on desalination - a figure which is expected to increase four-fold over the next six years. According to The Sunday Times, producing 100 million cubic metres of water by desalination costs Dh260m. If successful, Meteo's Weathertec system could produce the same amount for just Dh35m.

"If", however, is the key word. The results claimed by the newspaper were impressive, even alarming. The "secret project" was said to have "caused more than 50 rainstorms … and sparked concern over the violence of some of the storms, which included gales and lightning". And yet independent scientists who have been observing the project say there is no evidence that last summer's unusually high rainfall was triggered by Meteo's giant umbrellas. That, however, didn't stop a trickle of interest in the story turning into a flood of coverage, echoed in newspapers, magazines and blogs around the world.

Most of the information in the original article, headlined "Looks like rain: science creates desert downpours", appeared to have been gleaned from "a confidential company video" seen by the journalists. Though not quoted directly, the central figure in The Sunday Times story was Helmut Fluhrer, the founder of Meteo Systems. Since his brush with worldwide fame, Fluhrer has gone to ground. Every page on his company's website is password protected, except for a generalised introduction. "Some 19 per cent of global water is contained in the atmosphere as water vapour," it explains. "Very little of this huge supply of atmospheric water falls as precipitation in the right amounts and the right places. This is the challenge Weathertec is addressing."

According to The Sunday Times, "Scientists linked to Germany's Max Planck Institute for Meteorology - one of the world's leading centres for atmospheric physics - monitored the Abu Dhabi project and said they were impressed". But news of its involvement with the project came as, well, news to the Hamburg-based institute. A few hours after I contacted it regarding this apparent endorsement, the institute issued a strongly worded statement. Its directors were "distressed to learn that our institute is associated with, and even implied to have endorsed, recent claims by [a] private firm to have induced rain where rain would not otherwise have formed, this summer over Abu Dhabi". On the contrary, said the statement, which was signed by three professors, "we tend to view the claims being made rather sceptically, in line with many other members of the scientific community".

The Sunday Times had quoted Professor Hartmut Grassl, a former director of the institute: "There are many, many applications," he was reported to have said on the company video. "One is getting water into a dry area. Maybe this is a most important point for mankind." And yet, said the institute, while Grassl was "a retired director of our institute, with expertise in cloud physics", the fact that he had commented on the study in the press and agreed to evaluate the scientific basis for the claims "in no way endorses the claim by the firm involved". The institute itself had "no connection whatsoever" to the work and had not "been privy to the underlying evidence that the company is using to support its claims".

The statement also cast doubt on the science underlying the project. In the past, it noted, "similar claims have not survived strong scientific scrutiny," and there was "a strong scientific basis for believing that the claims reported in the press either distort the work involved, or are related to a misinterpretation of natural variability". "Many people," sniffed the institute, "have a financial stake in seeing these claims being credibly reported by the media."

By chance, the thorny question of how to distinguish the effects of such experiments from naturally occurring rainfall was addressed by the World Meteorological Organisation's Expert Team on Weather Modification Research at a two-day meeting in Abu Dhabi in March last year. In its final report, the meeting cast doubt on the efficacy of all forms of weather modification. It concluded that even the better established techniques for "purposeful augmentation of precipitation", such as cloud seeding, remained developing technologies which were "still striving to achieve a sound scientific foundation". When it came to creating rain clouds from scratch, "weather modification technologies that claim to achieve such ... dramatic effects do not have a sound scientific basis (e.g. hail canons, ionisation methods) and should be treated with suspicion".

There is no doubt that the number of rain showers in the Al Ain area was unusual this summer. And yet, as the Max Planck Institute noted, "they accompanied rather unusual weather patterns over the region, which certainly had nothing to do with the very localised experiments in Abu Dhabi. One only needs to be reminded of the terrible flooding over neighbouring Pakistan."

Meteo's claims, reported The Sunday Times, had "been backed by others", including Professor Peter Wilderer, the director of the Institute for Advanced Study at the Technical University of Munich. He reportedly observed the experiments. In fact, as Wilderer told me, "I have never eye-witnessed a rainfall event triggered by the company Meteo Systems. I just visited the Al Ain site once, but it didn't rain on that day." He had seen the article and in his view it gave "a false impression". Furthermore, he added, "I am not an expert in atmospheric physics, neither do I have knowledge about ionisation. My expertise is in water quality management."

Like Fluhrer, Grassl was also lying low, but he agreed to talk to me. Fluhrer, he said, "was very upset about this publicity … He told me he is hiding because he was upset about this leakage; he knows how science works and he knows that this [experiment] may die away, as is normal". Grassl said he had no financial involvement with Meteo Systems but had agreed to act as an independent observer and had visited Al Ain twice in that capacity, visiting one ionisation station on the slopes of Jebel Hafeet. "I am just a scientist keen to see if this system is good or not," he said. In fact, he is slightly more than just a scientist; in the 1990s he was director of the World Meteorological Organisation's climate research programme.

According to Grassl, Meteo was approaching the project openly and scientifically, and had invited a number of scientists to study the trials, agreeing they could publish papers about the outcome, whether positive or negative. Meanwhile there had, he agreed, been "some very heavy showers during this summer ... Observations at the sites measured the precipitation and in some cases it was 20mm of rain in half an hour, which is quite substantial". Yet without other, contextual data this proved nothing. Such heavy showers in the area were "really rare; maybe one event per year in June to August, but there are years when you have four or five of these events". Last summer there were even more; radar images had shown about 50 days of precipitation, though "most did not reach the ground because it is extremely hot".

"Now, if you were the boss of such a company," Grassl said, "you might say, 'Aha, we have made it'. But if you were a scientist you would say, 'Nearby in Pakistan, there was a [once every ] 1,000-year flooding event'. That is why when we were there last time we said you have to look into the long-term reanalysis data … This is a scientific activity, so you cannot do it from today until the next week, you need to work over months, at least."

Nothing more will be known until the independent scientists reconvene in Germany, probably before the spring. "When you have a chain of arguments and you have maybe seven hurdles over which you have to go, and the first three are OK, then you should publish. I am feeling this is the situation now," said Grassl. "My feeling is we have already enough for a first paper."

That, however, still leaves the possibility that the experiments could end in failure. "The probability that nothing is shown is higher than the probability that something is shown," Grassl observed. "It is always like this in science."

Another of the scientists who is monitoring the Al Ain trials is Axel Kleidon, a specialist in biospheric theory and modelling at the Max Planck Institute for Biogeochemistry in Jena, Germany. He is expected to be one of the lead authors of any paper produced by the independent observers.

"I hope that we have more to say and [will have] written up some results by the summer," he said. "All I can say at this time is that, yes, we are involved in assessing Meteo System's technology, some initial observations are encouraging, but these are still far from being scientifically conclusive."

For now, at least, the rain in Al Ain falls mainly in the imagination of journalists.